EP1335014B1 - Liquid crystalline medium - Google Patents

Abstract

A liquid crystal medium based on a mixture of polar compounds with positive dielectric anisotropy also contains (i) one or more ester compounds and (ii) one or more 4-ring compounds. A liquid crystal medium based on a mixture of polar compounds with positive dielectric anisotropy also contains: (i) one or more ester compounds of formula (I) and (ii) one or more 4-ring compounds of formula (II). R1 and R2 = H or 1-15C alkyl (optionally substituted by halogen and optionally with one or more -CH2- groups replaced by -C-triple bond-C-, -CH=CH-, -O-, -CO-O- or -O-CO- such that O atoms are not directly bonded with each other); X1 and X2 = F, Cl, CN, SF6, SCN, NCS or up to 6C halo-alkyl, -alkenyl, -alkoxy or -alkenyloxy; Z1 and Z2 = -CF2O-, -OCF2- or a single bond but are not the same; rings A and B = 1,4-cyclohexylene, 1,4-phenylene or a group of formula (III)-(VIII); and L1-L6 = H or F.

Description

The present invention relates to a liquid-crystalline medium and its use for electro-optical purposes and displays containing this medium.

Liquid crystals are mainly used as dielectrics in display devices, since the optical properties of such substances can be influenced by an applied voltage. Electro-optical devices based on liquid crystals are well recognized by the person skilled in the art and can be based on various effects. Such devices include, for example, dynamic scattering cells, DAP cells (upright phase deformation), guest / host cells, twisted nematic (TN) cells, super-twisted nematic (STN) cells, SBE cells ("superbirefringence effect") and OMI cells ("optical mode interference"). The most common display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.

The liquid crystal materials must have good chemical and thermal stability and good stability against electric fields and electromagnetic radiation. Further, the liquid crystal materials should have low viscosity and provide short response times, low threshold voltages, and high contrast in the cells.

Furthermore, they should have a suitable mesophase at normal operating temperatures, ie in the widest possible range below and above room temperature, for example, for the above-mentioned cells a nematic or cholesteric mesophase. Since liquid crystals are generally used as mixtures of several components, it is important that the components are readily miscible with each other. Other properties, such as electrical conductivity, dielectric anisotropy and optical anisotropy, must meet different requirements depending on the type of cell and the field of application. For example, materials for cells should be twisted with nematic structure have a positive dielectric anisotropy and a low electrical conductivity.

For example, for matrix liquid crystal displays with integrated non-linear elements for single pixel switching (MFK displays), media with high positive dielectric anisotropy, broad nematic phases, relatively low birefringence, very high resistivity, good UV and temperature stability and lower vapor pressure are desired ,

1. 1. MOS (Metal Oxide Semiconductor) oder andere Dioden auf Silizium-Wafer als Substrat.
2. 2. Dünnfilm-Transistoren (TFT) auf einer Glasplatte als Substrat.

Such matrix liquid crystal displays are known. As non-linear elements for individual switching of the individual pixels, for example, active elements (ie transistors) can be used. One speaks then of an "active matrix", whereby one can distinguish two types:

1. 1. MOS (Metal Oxide Semiconductor) or other diodes on silicon wafer as a substrate.
2. 2. Thin-film transistors (TFT) on a glass plate as a substrate.

The use of monocrystalline silicon as a substrate material limits the display size, since the modular composition of various partial displays on the joints leads to problems.

In the more promising type 2, which is preferred, the TN effect is usually used as the electro-optical effect. A distinction is made between two technologies: TFTs of compound semiconductors, such as e.g. CdSe or TFTs based on polycrystalline or amorphous silicon. The latter technology is being worked on worldwide with great intensity.

The TFT matrix is applied on the inside of one glass plate of the display, while the other glass plate on the inside carries the transparent counter electrode. Compared to the size of the pixel electrode, the TFT is very small and practically does not disturb the image. This technology can also be used for full color image reproduction be extended, wherein a mosaic of red, green and blue filters is arranged such that each one filter element is opposite to a switchable pixel.

The TFT displays usually operate as TN cells with crossed polarizers in transmission and are backlit.

The term MFK displays here includes any matrix display with integrated nonlinear elements, i. in addition to the active matrix also displays with passive elements such as varistors or diodes (MIM = metal-insulator-metal).

Such MFK displays are particularly suitable for TV applications (eg pocket TV) or for high-information displays for computer applications (laptop) and in the automotive or aircraft. In addition to problems with regard to the angle dependence of the contrast and the switching times, difficulties arise in the case of MFK displays due to the insufficiently high specific resistance of the liquid-crystal mixtures [ TOGASHI, S., SEKOGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, Sept. 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff, par is; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Liquid Crystal Displays, p. 145 ff, par is]. With decreasing resistance, the contrast of a MFK display deteriorates and the problem of "after image elimination" may occur. Since the resistivity of the liquid crystal mixture decreases by interaction with the internal surfaces of the display, generally over the lifetime of an MFK display, high (initial) resistance is very important in order to obtain acceptable service lives. In particular, in low-volt mixtures, it has not been possible to realize very high resistivities. Furthermore, it is important that the resistivity shows the smallest possible increase with increasing temperature and after temperature and / or UV exposure. Also particularly disadvantageous are the low-temperature properties of the mixtures of the prior art. It is required that also at Crystallization and / or smectic phases occur at low temperatures and the temperature dependence of the viscosity is as low as possible. The MFK displays from the prior art thus do not meet today's requirements.

Thus, there is still a great need for MFK displays with very high resistivity at the same time large working temperature range, short switching times even at low temperatures and low threshold voltage, which do not show these disadvantages or only to a lesser extent.

In addition to liquid crystal displays which use backlighting, ie are operated transmissively and optionally transflectively, reflective liquid crystal displays are also of particular interest. These reflective liquid crystal displays use the ambient light for information presentation. Thus, they consume significantly less energy than backlit liquid crystal displays of appropriate size and resolution. Since the TN effect is characterized by a very good contrast, such reflective displays are still easy to read even in bright ambient conditions. This is already from simple reflective TN displays, as they are in z. As watches and calculators are used known. However, the principle is also on high-quality, higher-resolution active matrix driven displays, such. As TFT displays, applicable. Here, as with the general conventional transmissive TFT-TN displays, the use of liquid crystals with low birefringence (Δn) is necessary to achieve a low optical delay (d An). This small optical delay leads to a mostly acceptable low viewing angle dependence of the contrast (cf. DE 30 22 818 ). For reflective displays, the use of liquid crystals with low birefringence is even more important than for transmissive displays, because with reflective displays the effective layer thickness through which the light passes is approximately twice that of transmissive displays with the same layer thickness.

• erweiterter nematischer Phasenbereich (insbesondere zu tiefen Temperaturen)
• lagerstabil, auch bei extrem tiefen Temperaturen
• Schaltbarkeit bei extrem tiefen Temperaturen (out-door-use, Automobil, Avionik)
• erhöhte Beständigkeit gegenüber UV-Strahlung (längere Lebensdauer)
• kleine optische Doppelbrechung (Δn) für reflektive Anzeigen

In TN (Schadt-Helfrich) cells, media are desired which allow the following advantages in the cells:

• extended nematic phase range (especially at low temperatures)
• stable on storage, even at extremely low temperatures
• Switchability at extremely low temperatures (out-door-use, automotive, avionics)
• increased resistance to UV radiation (longer life)
• small optical birefringence (Δn) for reflective displays

With the media available from the prior art, it is not possible to realize these advantages while maintaining the other parameters.

In the case of higher-twisted cells (STN), media are desired which enable higher multiplexability and / or lower threshold voltage and / or broader nematic phase ranges (in particular at low temperatures). For this purpose, a further expansion of the available parameter space (clearing point, transition smectic-nematic or melting point, viscosity, dielectric values, elastic sizes) is urgently desired.

The invention has for its object to provide media, in particular for such MFK, TN or STN displays, which do not or only to a lesser extent, the disadvantages mentioned above, and preferably at the same time very low threshold voltages and high values for the voltage holding Ratio (VHR).

It has now been found that this object can be achieved if used in ads according to the invention media.

und eine oder mehrere Verbindungen der Formel IA

enthält, worin die einzelnen Reste folgende Bedeutungen besitzen:

R¹ und R²

jeweils unabhängig voneinander H, einen halogenierten oder unsubstituierten Alkylrest mit 1 bis 15 C-Atomen, wobei in diesen Resten auch eine oder mehrere CH₂-Gruppen jeweils unabhängig voneinander durch -C≡C-, -CH=CH-, -O-, -CO-O-oder -O-CO- so ersetzt sein können, dass O-Atome nicht direkt miteinander verknüpft sind,

X¹ und X²

jeweils unabhängig voneinander F, Cl, CN, SF₅, SCN, NCS, halogenierter Alkylrest, halogenierter Alkenylrest, halogenierter Alkoxyrest oder halogenierter Alkenyloxyrest mit jeweils bis zu 6 C-Atomen,

Z¹ und Z²

jeweils unabhängig voneinander -CF₂O-, -OCF₂- oder eine Einfachbindung, wobei Z¹ ≠ Z² ist,

jeweils unabhängig voneinander

L^1-6

jeweils unabhängig voneinander H oder F.

The invention thus relates to a liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterized in that it contains one or more ester compounds of the formula I.

and one or more compounds of the formula IA

contains, in which the individual radicals have the following meanings:

R ¹ and R ²

in each case independently of one another H, a halogenated or unsubstituted alkyl radical having 1 to 15 C atoms, where in these radicals also one or more CH ₂ groups are each independently denoted by -C≡C-, -CH = CH-, -O-, -CO-O or -O-CO- may be replaced so that O atoms are not directly linked to each other,

X ¹ and X ²

each independently of one another F, Cl, CN, SF ₅ , SCN, NCS, halogenated alkyl radical, halogenated alkenyl radical, halogenated alkoxy radical or halogenated alkenyloxy radical having in each case up to 6 C atoms,

Z ¹ and Z ²

each independently represents -CF ₂ O-, -OCF ₂ - or a single bond, where Z ¹ ≠ Z ^2,

each independently

L ^1-6

each independently of one another H or F.

The compounds of the formulas I and IA have a wide range of applications. Depending on the choice of substituents, these compounds may serve as base materials from which liquid crystalline media are predominantly composed; However, it is also possible to add compounds of the formulas I and IA to liquid-crystalline base materials from other classes of compounds in order, for example, to influence the dielectric and / or optical anisotropy of such a dielectric and / or to optimize its threshold voltage and / or its viscosity.

The compounds of the formulas I and IA are colorless in the pure state and form liquid-crystalline mesophases in a temperature range which is favorably located for the electro-optical use. Chemically, thermally and against light, they are stable.

If R ¹ and / or R ^{2 are} an alkyl radical and / or an alkoxy radical, this may be straight-chain or branched. Preferably, it is straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and thus preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl , Octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradedoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (= methoxymethyl), 2 - (= ethoxymethyl) or 3-oxybutyl (= 2-methoxyethyl), 2-, 3- or 4-oxypentyl, 2-, 3-, 4- or 5- Oxyhexyl, 2-, 3-, 4-, 5- or 6-oxyheptyl, 2-, 3-, 4-, 5-, 6-, or 7-oxo-octyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadexyl.

If R ¹ and / or R ² denote an alkyl radical in which one CH ₂ group has been replaced by -CH = CH-, this may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 C atoms. It therefore means especially vinyl, prop-1, or prop-2-enyl, but-1, 2- or but-3-enyl, pent-1, 2-, 3- or pent-4-enyl, hex 1-, 2-, 3-, 4- or hex-5-enyl, hept-1, 2-, 3-, 4-, 5- or hept-6-enyl, Oct-1, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, Dec-1 -, 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl.

If R ¹ and / or R ² denote an alkyl radical in which one CH ₂ group has been replaced by -O- and one by -CO-, these are preferably adjacent. Thus, they include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably, these are straight-chain and have 2 to 6 carbon atoms. They therefore mean especially acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 2-acetyloxypropyl, 3-propionyl-oxypropyl, 4-acetyl-oxybutyl, Methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethly, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) -ethyl, 3- (methoxycarbonyl) -propyl, 3- (ethoxycarbonyl) -propyl or 4- (methoxycarbonyl) -butyl.

If R ¹ and / or R ² denote an alkyl radical in which one CH ₂ group is replaced by unsubstituted or substituted -CH = CH- and one adjacent CH ₂ group by CO or CO-O or O-CO, then this be straight-chain or branched. It is preferably straight-chain and has 4 to 12 C atoms. It therefore particularly means acryloyloxymethyl, 2-acryloyl-oxyethyl, 3-acryloyloxypropyl, 4-acryoyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyl-oxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyl-oxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryl-oyloxypentyl, 6-methacryloyloxyhexyl, 7 Methacryloyloxyheptyl, 8-methacryloyloxyoctyl, 9-methacryloyloxynonyl.

If R ¹ and / or R ^{2 are} an alkyl or alkenyl radical which is monosubstituted by CN or CF ₃ , this radical is preferably straight-chain. The substitution by CN or CF ₃ is in any position.

If R ¹ and / or R ^{2 are} an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain and halogen is preferably F or Cl. In the case of multiple substitution, halogen is preferably F. The resulting radicals also include perfluorinated radicals. For single substitution, the fluoro or chloro substituent may be in any position, but preferably in the ω position.

Compounds with branched wing groups R ¹ and / or R ² may occasionally be of importance for better solubility in the usual liquid-crystalline base materials, but especially as chiral dopants, if they are optically active. Smectic compounds of this type are useful as components of ferroelectric materials.

Branched groups of this type usually contain no more than one chain branch. Preferably branched radicals R ¹ and / or R ² are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl , 2-ethylhexyl, 2-propyl-pentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy.

If R ¹ and / or R ^{2 represent} an alkyl radical in which two or more CH ₂ groups have been replaced by -O- and / or -CO-O-, this may be straight-chain or branched. Preferably, it is branched and has 3 to 12 carbon atoms. It therefore particularly means bis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxypentyl, 6,6-bis-carboxy-hexyl, 7,7-bis-carboxyheptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxy-decyl, bis (methoxycarbonyl) -methyl, 2,2-bis (methoxycarbonyl) ethyl, 3,3-bis (methoxycarbonyl) propyl, 4,4-bis (methoxycarbonyl) butyl, 5,5-bis (methoxycarbonyl) pentyl, 6,6-bis (methocycarbonyl) hexyl, 7,7-bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) octyl, bis (ethoxycarbonyl) methyl, 2 , 2-bis- (ethoxycarbonyl) -ethyl, 3,3-bis (ethoxycarbonyl) -propyl, 4,4-bis (ethoxycarbonyl) -butyl, 5,5-bis (ethoxycarbonyl) -hexyl.

The compounds of the formulas I and IA are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg Thieme Verlag, Stuttgart) under reaction conditions which are known and suitable for the said reactions. One can also make use of known per se, not mentioned here variants. The compounds of the formula IA are, for. B. known from the published patent applications DE 40 06 921 . EP 1 046 693 A1 and EP 1 046 694 A1 ,

The invention also provides electro-optical displays (in particular STN or MFK displays with two plane-parallel support plates, which form a cell with a border, integrated non-linear elements for switching individual pixels on the support plates and a nematic liquid crystal mixture in the cell with positive dielectric anisotropy and high resistivity) containing such media as well as the use of these media for electro-optical purposes.

The liquid-crystal mixtures according to the invention enable a significant expansion of the available parameter space. The achievable combinations of clearing point, low temperature viscosity, thermal and UV stability, and dielectric anisotropy far surpass existing prior art materials.

Opposite from the EP 1 046 693 A1 In the case of the mixtures disclosed, the mixtures according to the invention have a higher clearing point, low γ ₁ values and very high values for the VHR at 100 ° C. The mixtures according to the invention are preferably suitable as TN-TFT mixtures for Note PC applications with 3.3 and 2.5 V drift.

The requirement for a high clearing point, nematic phase at low temperature and a high Δε has so far been insufficiently fulfilled. Systems such as e.g. Although ZLI-3119 have a comparable clearing point and comparable favorable viscosities, but have a Δε of only +3.

Other mixing systems have comparable viscosities and values of Δε, but have only clearing points in the region of 60 ° C.

The liquid-crystal mixtures according to the invention make it possible to maintain the nematic phase at -20 ° C. and preferably at -30 ° C., more preferably at -40 ° C., clearing point above 60 ° C., preferably above 65 ° C., particularly preferably above 70 ° C. simultaneously achieve dielectric anisotropy values Aε ≥ 6, preferably ≥ 8 and a high value for the resistivity, whereby excellent STN and MFK displays can be achieved. In particular, the mixtures are characterized by low operating voltages. The TN thresholds are below 2.0 V, preferably below 1.5 V, particularly preferably <1.3 V.

It is understood that by suitable choice of the components of the mixtures according to the invention also higher clearing points (eg above 110 ° C) can be realized at higher threshold voltages or lower clearing points at lower threshold voltages while maintaining the other advantageous properties. Likewise, with correspondingly low viscosities, mixtures with a larger Δε and thus lower thresholds can be obtained. The MFK displays according to the invention preferably operate in the first transmission minimum according to Gooch and Tarry [ CH Gooch and HA Tarry, Electron. Lett. 10, 2-4, 1974 ; CH Gooch and HA Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975 ]
Here, in addition to particularly favorable electro-optical properties, such as high slope of the characteristic and low angle dependence of the contrast ( DE-PS 30 22 818 ) at the same threshold voltage as in an analog display in the second minimum, a smaller dielectric anisotropy is sufficient. As a result, significantly higher specific resistances can be achieved using the mixtures according to the invention in the first minimum than in the case of mixtures with cyano compounds. By suitable choice of the individual components and their proportions by weight, the person skilled in the art can set the birefringence required for a given layer thickness of the MFK display with simple routine methods.

The flow viscosity ν ₂₀ at 20 ° C is preferably <60 mm ² -s ^-1 , more preferably <50 mm ² -s ^-1 . The rotational viscosity γ _{1 of} the mixtures according to the invention at 20 ° C. is preferably <160 mPa · s, more preferably <150 mPa · s. The nematic phase range is preferably at least 90 °, in particular at least 100 °. Preferably, this range extends at least from -20 ° to + 80 °.

For liquid crystal displays, a small switching time is desired. This is especially true for ads that are capable of video playback. For such displays, switching times (sum: t _on + t _off ) of a maximum of 16 ms are required. The upper limit of the switching time is determined by the refresh rate.

oder Ester der Formel

Measurements of the Voltage Holding Ratio (HR) [ S. Matsumoto et al., Liquid Crystals 5, 1320 (1989 ); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984 ); G. Weber et al., Liquid Crystals 5, 1381 (1989 )] have shown that mixtures according to the invention comprising compounds of the formula I and IA have a significantly smaller decrease in HR with increasing temperature than analogous mixtures comprising instead of the compounds of the formula IA Cyanophenylcyclohexanes of the formula

or esters of the formula

The UV stability of the mixtures according to the invention is also considerably better, i. they show a much smaller decrease in HR under UV exposure.

worin R¹ die in Anspruch 1 angegebenen Bedeutungen besitzt. Vorzugsweise bedeutet R¹ H, CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, n-C₆H₁₃, CH₂=CH, CH₃CH=CH oder 3-Alkenyl.Formula I preferably comprises the following compounds

wherein R ^{1 has} the meanings given in claim 1. Preferably, R ^{1 is} H, CH ₃ , C ₂ H ₅ , nC ₃ H ₇ , nC ₄ H ₉ , nC ₅ H ₁₁ , nC ₆ H ₁₃ , CH ₂ = CH, CH ₃ CH = CH or 3-alkenyl.

Preference is given to media according to the invention which comprise at least one compound of the formula I-1, I-2, I-8 and / or I-11, particularly preferably in each case at least one compound of the formula I-2.

worin R² die oben angegebenen Bedeutungen hat.Particularly preferred compounds of the formula IA are compounds of the formulas IA-1 to IA-25:

wherein R ^{2 has} the meanings given above.

Of these preferred compounds, particular preference is given to those of the formulas IA-1, IA-2, IA-3, IA-4 and IA-15, in particular those of the formulas IA-1 and IA-2.

R ² in the compounds of the formulas IA and IA1 to IA-24 preferably denotes H, straight-chain alkyl having 1 to 7 C atoms, in particular CH ₃ , C ₂ H ₅ , nC ₃ H ₇ , NC ₄ H ₉ , nC ₅ H ₁₁ , nC ₆ H ₁₃ , nC ₇ H ₁₅ , furthermore 1 E- or 3-alkenyl, especially CH ₂ = CH, CH ₃ CH = CH, CH ₂ = CHCH ₂ CH ₂ , CH ₃ CH = CH-CH ₂ CH ₂ .

The compounds of the formula IA are, for. B. from known EP 0 334 911 B1 and WO 01-25370 ,

• Das Medium enthält ein, zwei oder mehr Verbindungen ausgewählt aus der Gruppe der Formeln IA-1 bis IA-24;
• Das Medium enthält vorzugsweise jeweils eine oder mehrere, vorzugsweise zwei oder drei, Verbindungen (Homologen) der Formeln I-2 und IA-15;
• Das Medium enthält vorzugsweise jeweils eine oder mehrere, vorzugsweise zwei oder drei, Verbindungen (Homologen) der Formeln 1-2 und IA-3;
• Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den allgemeinen Formeln II bis VI:
  
  
  
  
  

worin die einzelnen Reste die folgenden Bedeutungen haben:

R⁰

n-Alkyl, Oxaalkyl, Fluoralkyl oder Alkenyl mit jeweils bis zu 9 C-Atomen,

X⁰

F, Cl, halogeniertes Alkyl, Alkenyl, Alkenyloxy oder Alkoxy mit bis zu 6 C-Atomen,

Z⁰

-C₂F₄-, -CF=CF-, -C₂H₄-, -(CH₂)₄-, -CF₂O-, -OCF₂-, -OCH₂- oder -CH₂O-,

Y¹ bis Y⁴

jeweils unabhängig voneinander H oder F,

r

0 oder 1.

Preferred embodiments are given below:

• The medium contains one, two or more compounds selected from the group of the formulas IA-1 to IA-24;
• The medium preferably contains in each case one or more, preferably two or three, compounds (homologues) of the formulas I-2 and IA-15;
• The medium preferably contains one or more, preferably two or three, compounds (homologues) of formulas 1-2 and IA-3;
• The medium additionally contains one or more compounds selected from the group consisting of the general formulas II to VI:
  
  
  
  
  

in which the individual radicals have the following meanings:

R ⁰

n-alkyl, oxaalkyl, fluoroalkyl or alkenyl having in each case up to 9 C atoms,

X ⁰

F, Cl, halogenated alkyl, alkenyl, alkenyloxy or alkoxy having up to 6 C atoms,

Z ⁰

-C ₂ F ₄ -, -CF = CF-, -C ₂ H ₄ -, - (CH ₂ ) ₄ -, -CF ₂ O-, -OCF ₂ -, -OCH ₂ - or -CH ₂ O-,

Y ¹ to Y ⁴

each independently of one another H or F,

r

0 or 1.

• Das Medium enthält zusätzlich eine oder mehrere Verbindungen ausgewählt aus der Gruppe bestehend aus den allgemeinen Formeln VII bis XIII:
  
  
  
  
  
  
  

worin R⁰, X⁰, Y¹ und Y² jeweils unabhängig voneinander eine der in Anspruch 4 angegebenen Bedeutung haben. Y³ bedeutet H oder F. X⁰ ist vorzugsweise F, Cl, CF₃, OCF₃ oder OCHF₂. R⁰ bedeutet vorzugsweise Alkyl, Oxaalkyl, Fluoralkyl oder Alkenyl mit jeweils bis zu 6 C-Atomen.

• Das Medium enthält zusätzlich eine oder mehrere EsterVerbindungen der Formeln Ea bis Ed,
  
  
  
  

worin R⁰ die in Anspruch 4 angegebene Bedeutung hat;The compound of formula IV is preferred

• The medium additionally contains one or more compounds selected from the group consisting of the general formulas VII to XIII:
  
  
  
  
  
  
  

wherein R ⁰ , X ⁰ , Y ¹ and Y ² each independently have one of the meanings given in claim 4. Y ³ is H or F. X ⁰ is preferably F, Cl, CF ₃ , OCF ₃ or OCHF ₂ . R ⁰ is preferably alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 6 C atoms.

• The medium additionally contains one or more ester compounds of the formulas Ea to Ed,
  
  
  
  

wherein R ^{0 has} the meaning given in claim 4;

• Der Anteil an Verbindungen der Formeln IA und I bis VI zusammen beträgt im Gesamtgemisch mindestens 50 Gew.%;
• Der Anteil an Verbindungen der Formel I beträgt im Gesamtgemisch 5 bis 40, besonders bevorzugt 10 bis 30 Gew.%;
• Der Anteil an Verbindungen der Formel IA beträgt im Gesamtgemisch 5 bis 40, besonders bevorzugt 10 bis 30 Gew.%;
• Der Anteil an Verbindungen der Formeln II bis VI im Gesamtgemisch beträgt 30 bis 80 Gew.%;
  
  
  
  
• Das Medium enthält Verbindungen der Formeln II, III, IV, V oder VI;
• R⁰ ist geradkettiges Alkyl oder Alkenyl mit 2 bis 7 C-Atomen;
• Das Medium besteht im wesentlichen aus Verbindungen der Formeln IA, I bis VI und XIII;
• Das Medium enthält weitere Verbindungen, vorzugsweise ausgewählt aus der folgenden Gruppe bestehend aus den allgemeinen Formeln XIV bis XVII:
  
  
  
  

worin R⁰ und X⁰ die oben angegebene Bedeutung haben und die 1,4-Phenylenringe durch CN, Chlor oder Fluor substituiert sein können. Vorzugsweise sind die 1,4-Phenylenringe ein- oder mehrfach durch Fluoratome substituiert.

• Das Medium enthält zusätzlich ein oder mehrere Verbindungen der Formeln XVIII
  

worin R⁰, X⁰, Y¹, Y² die oben angegebenen Bedeutungen haben.

• Das Medium enthält zusätzlich ein, zwei, drei oder mehr, vorzugsweise zwei oder drei, Verbindungen der Formel
  
  

worin "Alkyl" und "Alkyl*" die nachfolgend angegebene Bedeutung haben.The proportion of the compound of the formulas Ea to Ed is preferably 10-30% by weight, in particular 15-25% by weight;

• The proportion of compounds of the formulas IA and I to VI together in the total mixture is at least 50% by weight;
• The proportion of compounds of formula I is in the total mixture 5 to 40, particularly preferably 10 to 30 wt.%;
• The proportion of compounds of the formula IA is in the total mixture 5 to 40, particularly preferably 10 to 30 wt.%;
• The proportion of compounds of the formulas II to VI in the total mixture is 30 to 80% by weight;
  
  
  
  
• The medium contains compounds of the formulas II, III, IV, V or VI;
• R ⁰ is straight-chain alkyl or alkenyl having 2 to 7 C atoms;
• The medium consists essentially of compounds of the formulas IA, I to VI and XIII;
• The medium contains further compounds, preferably selected from the following group consisting of the general formulas XIV to XVII:
  
  
  
  

wherein R ⁰ and X ^{0 have} the abovementioned meaning and the 1,4-phenylene rings may be substituted by CN, chlorine or fluorine. Preferably, the 1,4-phenylene rings are mono- or polysubstituted by fluorine atoms.

• The medium additionally contains one or more compounds of the formulas XVIII
  

wherein R ⁰ , X ⁰ , Y ¹ , Y ^{2 have} the meanings given above.

• The medium additionally contains one, two, three or more, preferably two or three, compounds of the formula
  
  

wherein "alkyl" and "alkyl *" have the meaning given below.

• Das Medium enthält vorzugsweise 5-35 Gew.% der Verbindung IVa.
• Das Medium enthält vorzugsweise eine, zwei oder drei Verbindungen der Formel IVa, worin X° F oder OCF₃ bedeutet.
• Das Medium enthält vorzugsweise ein oder mehrere Verbindungen der Formeln lla bis IIg,
  
  
  
  
  
  
  

worin R⁰ die oben angegebenen Bedeutungen hat. In den Verbindungen der Formeln IIa-IIg bedeutet R⁰ vorzugsweise H, Methyl, Ethyl, n-Propyl, n-Butyl oder n-Pentyl, ferner n-Hexyl oder n-Heptyl.

• Das Gewichtsverhältnis (I + IA): (II + III + IV + V + VI) ist vorzugsweise 1 : 10 bis 10 : 1.
• Das Medium besteht im wesentlichen aus Verbindungen ausgewählt aus der Gruppe bestehend aus den allgemeinen Formeln IA und I bis XIII.
• Der Anteil der Verbindungen der Formel IVb und/oder IVc, worin X^o Fluor und R⁰ C₂H₅, n-C₃H₇, n-C₄H₅ oder n-C₅H₁₁ bedeutet, beträgt im Gesamtgemisch 2 bis 20 Gew.%, insbesondere 2 bis 15 Gew.%;
• Das Medium enthält vorzugsweise ein, zwei oder drei, ferner vier, Homologe der Verbindungen ausgewählt aus der Gruppe H1 bis H18 (n = 1-12):
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• Das Medium enthält weitere Verbindungen, vorzugsweise ausgewählt aus der folgenden Gruppe bestehend aus den allgemeinen Formeln XVI bis XIX:
  
  
  
  

worin R⁰ und X⁰ die oben angegebene Bedeutung haben und die 1,4-Phenylenringe durch CN, Chlor oder Fluor substituiert sein können. Vorzugsweise sind die 1,4-Phenylenringe ein- oder mehrfach durch Fluoratome substituiert.

• Das Medium enthält weitere Verbindungen, vorzugsweise ausgewählt aus der folgenden Gruppe bestehend aus den Formeln RI bis RVIII,
  
  
  
  
  
  
  
  
  
  worin

  R⁰

  n-Alkyl, Oxaalkyl, Fluoralkyl, Alkenyloxy oder Alkenyl mit jeweils bis zu 9 C-Atomen,

  Y¹

  H oder F,
  Alkyl oder

  Alkyl*

  jeweils unabhängig voneinander ein geradkettiger oder verzweigter Alkylrest mit 1-9 C-Atomen,
  Alkenyl oder

  Alkenyl*

  jeweils unabhängig voneinander einen geradkettigen oder verzweigten Alkenylrest mit bis zu 9 C-Atomen
  bedeuten.

• Das Medium enthält vorzugsweise ein oder mehrere Verbindungen der Formeln
  
  
  
  
  
  worin
  n und m jeweils 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 oder 12 bedeuten.
  Vorzugsweise ist n bis m 1, 2, 3, 4, 5 oder 6.
• Medium enthaltend zusätzlich ein, zwei oder mehr Verbindungen mit annellierten Ringen der Formeln AN1 bis AN11:
  
  
  
  
  
  
  
  
  
  
  

worin R⁰ die oben angegebenen Bedeutungen hat;The proportion of the compounds of the formulas O1 and / or O2 in the mixtures according to the invention is preferably 5-10% by weight.

• The medium preferably contains 5-35% by weight of compound IVa.
• The medium preferably contains one, two or three compounds of the formula IVa in which X is F or OCF ₃ .
• The medium preferably contains one or more compounds of the formulas IIa to IIg,
  
  
  
  
  
  
  

wherein R ^{0 has} the meanings given above. In the compounds of the formulas IIa-IIg, R ^{0 is} preferably H, methyl, ethyl, n-propyl, n-butyl or n-pentyl, furthermore n-hexyl or n-heptyl.

• The weight ratio (I + IA): (II + III + IV + V + VI) is preferably 1:10 to 10: 1.
• The medium consists essentially of compounds selected from the group consisting of the general formulas IA and I to XIII.
• The proportion of compounds of the formula IVb and / or IVc in which X ^{o is} fluorine and R ^{0 is} C ₂ H ₅ , nC ₃ H ₇ , nC ₄ H ₅ or nC ₅ H ₁₁ is 2 to 20% by weight in the total mixture, in particular 2 to 15% by weight;
• The medium preferably contains one, two or three, and further four, homologues of the compounds selected from the group H1 to H18 (n = 1-12):
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• The medium contains further compounds, preferably selected from the following group consisting of the general formulas XVI to XIX:
  
  
  
  

wherein R ⁰ and X ^{0 have} the abovementioned meaning and the 1,4-phenylene rings may be substituted by CN, chlorine or fluorine. Preferably, the 1,4-phenylene rings are mono- or polysubstituted by fluorine atoms.

• The medium contains further compounds, preferably selected from the following group consisting of the formulas RI to RVIII,
  
  
  
  
  
  
  
  
  
  wherein

  R ⁰

  n-alkyl, oxaalkyl, fluoroalkyl, alkenyloxy or alkenyl having in each case up to 9 C atoms,

  Y ¹

  H or F,
  Alkyl or

  alkyl *

  each independently of one another a straight-chain or branched alkyl radical having 1-9 C atoms,
  Alkenyl or

  alkenyl *

  each independently of one another a straight-chain or branched alkenyl radical having up to 9 C atoms
  mean.

• The medium preferably contains one or more compounds of the formulas
  
  
  
  
  
  wherein
  n and m are each 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.
  Preferably, n to m is 1, 2, 3, 4, 5 or 6.
• Medium containing in addition one, two or more compounds with fused rings of the formulas AN1 to AN11:
  
  
  
  
  
  
  
  
  
  
  

wherein R ^{0 has} the meanings given above;

It has been found that even a relatively small proportion of compounds of the formulas I and IA in admixture with conventional liquid crystal materials, but in particular with one or more compounds of the formulas II, III, IV, V and / or VI to a considerable lowering of the threshold voltage and to high values for the VHR (100 ° C), while simultaneously observing broad nematic phases with low transition temperatures smectic-nematic, thereby improving storage stability. Particular preference is given to mixtures which, in addition to one or more compounds of the formulas I and IA, contain one or more compounds of the formula IV, in particular compounds of the formula IVa in which X ⁰ denotes F or OCF ₃ . The compounds of the formulas IA, I to VI are colorless, stable and readily miscible with one another and with other liquid crystal materials.

The term "alkyl" or "alkyl *" embraces straight-chain and branched alkyl groups having 1-7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups of 2-5 carbon atoms are generally preferred.

The term "alkenyl" includes straight-chain and branched alkenyl groups having 2-7 carbon atoms, especially the straight-chain groups. Preferred alkenyl groups are C ₂ -C ₇ -1E-alkenyl, C ₄ -C ₇ -E-alkenyl, C ₅ -C ₇ -alkenyl, C ₆ -C ₇ -5-alkenyl and C ₇ -6-alkenyl, in particular C ₂ -C ₇ -1E alkenyl, C ₄ -C ₇ 3E alkenyl and C ₅ -C ₇ 4 alkenyl. Examples of particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4- Pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups of up to 5 carbon atoms are generally preferred.

The term "fluoroalkyl" preferably includes straight-chain fluoro-terminated groups, i. Fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. Other positions of the fluorine are not excluded.

The term "oxaalkyl" preferably includes straight-chain radicals of the formula C _n H _{2n + 1} -O- (CH ₂ ) _m , wherein n and m are each independently 1 to 6. Preferably, n = 1 and m is 1 to 6.

By suitably selecting the meanings of R ⁰ and X ⁰ , the response times, the threshold voltage, the transconductance of the transmission characteristics etc. can be modified in the desired manner. For example, 1 E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like usually lead to shorter response times, improved nematic tendencies and a higher ratio of the elastic constants k ₃₃ (bend) and k ₁₁ (splay) in comparison to alkyl resp Alkoxy radicals. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller values of k ₃₃ / k ₁₁ compared to alkyl and alkoxy radicals.

A -CH ₂ CH ₂ group generally results in higher values of k ₃₃ / k ₁₁ compared to a single covalent bond. Higher values of k ₃₃ / k ₁₁ facilitate, for example, flatter transmission characteristic lines in TN cells with a 90 ° twist (for achieving gray shades) and steeper transmission characteristic lines in STN, SBE and OMI cells (greater multiplexing) and vice versa.

The optimum ratio of the compounds of the formulas I, IA and II + III + IV + V + VI depends largely on the desired properties, on the choice of the components of the formulas I, IA, II, III, IV, V and / or VI and the choice of other optionally present components.

Suitable proportions within the range given above can be easily determined on a case-by-case basis.

The total amount of compounds of the formulas IA and I to XIII in the mixtures according to the invention is not critical. The mixtures may therefore contain one or more other components to optimize various properties. However, the observed effect on the response times and the threshold voltage is generally greater the higher the total concentration of compounds of the formulas IA and I to XIII.

In a particularly preferred embodiment, the media of the invention comprise compounds of the formula II to VI (preferably II, III and / or IV, in particular IVa) wherein X ⁰ is F, OCF _3, OCHF _2, F, OCH = CF _2, OCF = CF ₂ or OCF ₂ -CF ₂ H.. A favorable synergistic effect with the compounds of the formulas I and IA leads to particularly advantageous properties. In particular, mixtures containing compounds of the formula I, IA and the formula IVa are distinguished by their low threshold voltage.

The individual compounds of the formulas IA and I to XVIII and their sub-formulas which can be used in the media according to the invention are either known or they can be prepared analogously to the known compounds.

The structure of the MFK display of polarizers, electrode base plates and electrodes with surface treatment according to the invention corresponds to the usual construction for such displays. Here, the term of the usual construction is broad and includes all modifications and modifications of the MFK display, in particular matrix display elements based on poly-Si TFT or MIM.

However, a significant difference of the displays of the invention on the basis of the usual twisted nematic cell is the choice of the liquid crystal parameters of the liquid crystal layer.

The preparation of the liquid crystal mixtures which can be used according to the invention is carried out in a conventional manner. In general, the desired amount of the components used in a lesser amount is dissolved in the component making up the main constituent, advantageously at elevated temperature. It is also possible to use solutions of the components in an organic solvent, e.g. in acetone, chloroform or methanol, and to remove the solvent again after thorough mixing, for example by distillation.

The dielectrics may also contain further additives known to the person skilled in the art and described in the literature. For example, 0-15% pleochroic dyes, antioxidants, UV absorbers, and / or chiral dopants may be added.

C is a crystalline, S is a smectic, S _{c is} a smectic C, N is a nematic and I is the isotropic phase.

V ₁₀ denotes the voltage for 10% transmission (viewing direction perpendicular to the plate surface). t _on denotes the switch-on time and t _off the switch-off time at an operating voltage corresponding to 2.0 times the value of V ₁₀ . Δn denotes the optical anisotropy. Δε denotes the dielectric anisotropy (Δε = ε _∥ - ε _⊥ , where ε _{∥ means} the dielectric constant parallel to the _longitudinal molecular _axes and ε _{⊥ means} the dielectric constant perpendicular thereto). The electro-optical data were measured in a TN cell in the 1st minimum (ie at a Δn value of 0.5 μm) at 20 ° C, unless expressly stated otherwise. The optical data were measured at 20 ° C unless expressly stated otherwise.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms,
wherein the transformation into chemical formulas according to the following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms; n and m are integers and are preferably 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. The coding according to Table B is self-evident. In Table A is only the acronym given for the basic body. In individual cases a code for the substituents R ¹ *, R ² *, L ¹ *, L ² * and L ³ * follows separately from Acronym for the main body with a rope: Code for R ¹ *, R ² *, L ¹ *, L ^{2 *} , L ^{3 *} R ^{1 *} R ^{2 *} L ^{1 *} L ^{2 *} L ^{3 *} nm CnH _{2n + 1} C _m H _{2m + 1} H H H n Om OC _n H _{2n + 1} C _m H _{2m + 1} H H H nO.m C _n H _{2n + 1} OC _m H _{2m + 1} H H H n C _n H _{2n + 1} CN H H H nN.F C _n H _{2n + 1} CN H H F nN.FF C _n H _{2n + 1} CN H F F nF C _n H _{2n + 1} F H H H nOF OC _n H _{2n + 1} F H H H nF.F C _n H _{2n + 1} FC _m H _{2m + 1} H H F NMF C _n H _{2n + 1} F H H nOCF ₃ C _n H _{2n + 1} OCF ₃ H H H nOCF ₃ .F C _n H _{2n + 1} OCF ₃ F H H n-Vm C _n H _{2n + 1} -CH = CH-C _m H _{2m + 1} H H H nV-Vm C _n H _{2n + 1} -CH = CH- -CH = CH-C _m H _{2m + 1} H H H

PYP

PYRP

BCH

CBC

CCH

CCP

CPTP

CEPTP

ECCP

CECP

EPCH

PCH

PTP

BECH

EBCH

CPC

B

FET-n-F

CGG

CGU

CFU

PGU Tabelle B:

BCH-n.Fm

CFU-n-F

CBC-nmF

ECCP-nm

CCZU-n-F

T-nFm

CGU-n-F

CDU-n-F

DCU-n-F

CGG-n-F

CPZG-n-OT

CC-nV-Vm

CCP-Vn-m

CCG-V-F

CCP-nV-m

CC-n-V

CCQU-n-F

CC-n-V1

CCQG-n-F

CQCU-n-F

Dec-U-n-F

CWCU-n-F

CWCG-n-F

CCOC-n-m

CPTU-n-F

GPTU-n-F

PQU-n-F

PUQU-n-F

PGU-n-F

CGZP-n-OT

CCGU-n-F

CCQG-n-F

CUQU-n-F

PUQU-n-F

CUQU-n-F

CGUQU-n-F

CCPU-n-F

CECU-n-F

CCEU-n-F

CPEU-n-F

CPUQU-n-F Preferred mixture components are given in Tables A and B. <b><u> Table A: </ u></b>

PYP

PYRP

BCH

CBC

CCH

CCP

CPTP

CEPTP

ECCP

CECP

EPCH

PCH

PTP

Bech

EBCH

CPC

B

FET nF

CGG

CGU

CFU

PGU

BCH-n.Fm

CFU-nF

CBC NMF

ECCP-nm

CCZU-nF

T-NFM

CGU-nF

CDU nF

DCU nF

CGG nF

CPZG-n-OT

CC-nV-Vm

CCP-Vn-m

CCG-VF

CCP-nV-m

CC-nV

CCQU-nF

CC-n-V1

CCQG nF

CQCU nF

Dec-UnF

CWCU nF

CWCG nF

CCOC nm

CPTU nF

GPTU nF

PQU nF

PUQU nF

PGU-nF

CGZP-n-OT

CCGU-nF

CCQG nF

CUQU nF

PUQU nF

CUQU nF

CGUQU nF

CCPU nF

CECU nF

CCEU nF

CPEU nF

CPUQU nF

C15

CB 15

CM 21

R/S-811

CM 44

CM 45

CM 47

R/S-1011

R/S-3011

CN

R/S-2011

Particular preference is given to liquid-crystalline mixtures which, in addition to the compounds of the formulas I and IA, contain at least one, two, three or four compounds from Table B. <b><u> Table C: </ u></b> In Table C possible dopants are given, which are usually added to the mixtures of the invention.

C15

CB 15

CM 21

R / S-811

CM 44

CM 45

CM 47

R / S-1011

R / S-3011

CN

R / S 2011

The following examples are intended to illustrate the invention without limiting it. Above and below, percentages are by weight. All temperatures are in degrees Celsius. Mp means Melting point, bp. Clearing point. Furthermore, K = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. Δn means optical anisotropy (589 nm, 20 ° C.), Δε the dielectric anisotropy (1 kHz, 20 ° C.), the flow viscosity ν ₂₀ (mm ² / sec) became 20 ° C determines. The rotational viscosity γ ₁ (mPa · s) was also determined at 20 ° C. <u> Example M1 </ u> PUQU-3-F 7.00% Clearing point [° C]: +70 BCH 3F.FF 5.50% Δn [589 nm; 20 ° C]: +0.0932 CUQU-3-F 5.00% Δε [1 kHz; 20 ° C]: 13.5 CCP 2F.F 12.00% VHR (100 ° C): 94.5 CCP 3F.FF 10.00% γ ₁ [mPa · s; 20 ° C]: 159 CECG-3-F 10.00% V _10,0,20 : 0.94 CCZU-3-F 13.00% CCZU-4-F 5.00% CDU-3-F 3.00% DCU-4-F 6.00% CGUQU-2-F 8.50% CGUQU-3-F 4.00% CGZP-2-OT 6.00% CGZP-3-OT 5.00% CC-3-V 16.00% S → N [° C]: -40.0 CCZU-2-F 4.00% Clearing point [° C]: +79.0 CCZU-3-F 15.00% Δn [589 nm; 20 ° C]: +0.0883 CGZP-2-OT 10.00% VHR (100 ° C): 94.6 CDU-2-F 7.00% γ ₁ [mPa · s; 20 ° C]: 127 CDU-3-F 9.00% V _10,0,20 : 1.04 CDU-5-F 9.00% CCH-35 5.00% CGU-2-F 3.00% CC-3-V1 2.00% CPUQU-3-F 10.00% CPUQU-2-F 10.00% CC-3-V 19.00% S → N [° C]: -40.0 CCH-35 3.00% Clearing point [° C]: +79.0 CCZU-2-F 4.00% Δn [589 nm; 20 ° C]: +0.0887 CCZU-3-F 14.00% γ ₁ [mPa · s; 20 ° C]: 132 CGZP-2-OT 10.00% V _10,0,20 : 0.99 CGZP-3-OT 8.00% VHR (100 ° C): 94.5 CDU-2-F 9.00% γ ₁ [mPa · s; 20 ° C]: 159 CDU-3-F 9.00% V _10,0,20 : 0.94 CDU-5-F 4.00% CGUQU-2-F 10.00% CGUQU-3-F 10.00% Comparative Example (Example of p. 37 of EP 1 046 693) PUQU-3-F 4.0% Clearing point [° C]: +70.1 BCH 3F.FF 21.0% Δn [589 nm; 20 ° C]: +0.0926 CCPU-3-F 4.0% Δε [1 kHz; 20 ° C]: 12.0 CUQU-3-F 4.0% VHR (100 ° C): 90.8 CCP 2F.F 7.0% γ ₁ [mPa · s; 20 ° C]: 161 CCP 3F.F 7.0% V _10,0,20 : 1.01 CCP 3F.FF 8.0% CECU-3-F 10.0% CCEU-3-F 10.0% CCEU-4-F 3.0% CPEU-2-F 2.0% CPEU-3-F 3.0% CDU-3-F 3.0% DCU-4-F 7.0% DCU-5-F 7.0% CC-3-V 16.00% CCH-35 4.00% CCP 1F.FF 11.00% CCP 2F.FF 9.00% CCP 3F.FF 5.00% CCP-20CF ₃ .F 11.00% CCZU-2-F 4.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CGZP-2-OT 10.00% CPUQU-2-F 2.00% CPUQU-3-F 7.00% CCOC-3-3 2.00% CC-3-V1 3.00% CCH-35 4.00% CC V-5 12.00% CCH-3CF ₃ 4.00% CCP-1 FFF 11.00% CCP 2F.FF 9.00% CCP-20CF ₃ 5.00% CCP-20CF ₃ .F 6.00% CCZU-2-F 4.00% CCZU-3-F 15.00% CCZU-5-F 4.00% CGZP-2-OT 10.00% CGZP-3-OT 4.00% CPUQU-2-F 7.00% CCOC-3-3 2.00% CDU-2-F 9.00% CDU-3-F 9.00% PGU-2-F 9.00% PGU-3-F 6.00% CGZP-2-OT 10.00% CCZU-2-F 4.00% CCZU-3-F 15.00% CCZU-5-F 2.00% CC V-5 13.00% CC-3-V1 11.00% CCP-20CF ₃ 9.00% CPUQU-2-F 3.00% CC-3-V 15.00% S → N [° C]: -40.0 CCZU-2-F 4.00% Clearing point [° C]: +80.0 CCZU-3-F 14.00% Δn [589 nm; 20 ° C]: +0.0899 CGZP-2-OT 10.00% VHR (100 ° C): 92 CDU-2-F 7.00% γ ₁ [mPa · s; 20 ° C]: 119 CDU-3-F 8.00% HTP [20 ° C; microns]: 0.50 CDU-5-F 7.00% Twist [°]: 90 PGU-2-F 1.00% V ₁₀ [V]: 1.07 CCH-35 4.00% CGU-2-F 2.50% CC-3-V1 7.50% CPUQU-3-F 10.00% CPUQU-2-F 10.00% CCP-20CF ₃ 3.00% S → N [° C]: -40.0 CCP-30CF ₃ 7.00% Clearing point [° C]: +83.5 CCP-40CF ₃ 3.00% Δn [589 nm; 20 ° C]: +0.0805 CCZU-2-F 4.00% VHR (100 ° C): 98.6 CCZU-3-F 13.00% γ ₁ [mPa · s; 20 ° C]: 89 CGZP-2-OT 8.00% HTP [20 ° C; microns]: 0.50 CDU-2-F 9.00% Twist [°]: 90 CDU-3-F 6.00% V ₁₀ [V]: 1.30 CC-3-V1 12.00% CC-3-V 18.00% CCH-35 4.00% CGUQU-2-F 10.00% CGUQU-3-F 3.00% CC-3-V 18.00% S → N [° C]: -40.0 CCH-35 4.00% Clearing point [° C]: +80.0 CCZU-2-F 3.00% Δn [589 nm; 20 ° C]: +0.0890 CCZU-3-F 15.00% γ ₁ [mPa.s; 20 ° C]: 135 CGZP-2-OT 10.00% HTP [20 ° C; microns]: 0.50 CGZP-3-OT 7.50% Twist [°]: 90 CGU-2-F 0.50% V ₁₀ [V]: 1.00 CDU-2-F 8.00% CDU-3-F 8.00% CDU-5-F 6.00% CGUQU-2-F 10.00% CGUQU-3-F 10.00% CCP-20CF ₃ 7.00% S → N [° C]: -40.0 CCP-30CF ₃ 4.00% Clearing point [° C]: +80.5 CCP 2F.FF 3.00% Δn [589 nm; 20 ° C]: +0.0800 CCZU-2-F 4.00% γ ₁ [mPa · s; 20 ° C]: 90 CCZU-3-F 13.00% HTP [20 ° C; microns]: 0.50 CGZP-2-OT 6.00% Twist [°]: 90 CDU-2-F 7.00% V ₁₀ [V]: 1.28 CDU-3-F 7.00% CC-3-V1 11.00% CC-3-V 18.00% CCH-35 5.00% CGUQU-2-F 10.00% CGUQU-3-F 5.00%

Claims (11)

1. Liquid-crystalline medium based on a mixture of polar compounds of positive dielectric anisotropy, characterised in that it comprises one or more ester compounds of the formula I

   

   and one or more compounds of the formula IA

   

   in which the individual radicals have the following meanings:

   R¹ and R² each, independently of one another, denote H, a halogenated or unsubstituted alkyl radical having 1 to 15 C atoms, where one or more CH₂ groups in these radicals may also be replaced, in each case independently of one another, by -C≡C-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that O atoms are not linked directly to one another,

   X¹ and X² each, independently of one another, denote F, Cl, CN, SF₅, SCN, NCS, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated alkoxy radical or a halogenated alkenyloxy radical, each having up to 6 C atoms,

   Z¹ and Z² each, independently of one another, denote -CF₂O-, -OCF₂- or a single bond, where Z¹ ≠ Z²,

   

   

   

   L^1-6 each, independently of one another, denote H or F.
2. Liquid-crystalline medium according to Claim 1, characterised in that it comprises one, two or more compounds of the formulae IA1-IA25:

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   

   in which R² has the meaning indicated in Claim 1.
3. Liquid-crystalline medium according to Claim 1, characterised in that it comprises one or more compounds of the formulae I-1 to I-5

   

   

   

   

   

   in which R¹ has the meanings indicated in Claim 1.
4. Liquid-crystalline medium according to at least one of Claims 1 to 3, characterised in that it additionally comprises one or more compounds selected from the group consisting of the general formulae II, III, IV, V and VI:

   

   

   

   

   

   in which the individual radicals have the following meanings:

   R⁰ denotes H, n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having up to 9 C atoms,

   X⁰ denotes F, Cl, halogenated alkyl, alkenyl or alkoxy having up to 6 C atoms,

   Z⁰ denotes -C₂F₄-, -CF=CF-, -C₂H₄-, -(CH₂)₄-, -CF₂O-, -OCF₂-, -OCH₂- or -CH₂O-,

   Y¹ and Y² each, independently of one another, denote H or F, r denotes 0 or 1.
5. Medium according to Claim 4, characterised in that the proportion of compounds of the formulae IA and I to VI together in the mixture as a whole is at least 50% by weight.
6. Medium according to at least one of Claims 1 to 5, characterised in that it additionally comprises one or more compounds of the formulae Ea to Ed

   

   

   

   

   in which R⁰ has the meaning indicated in Claim 4.
7. Medium according to at least one of Claims 1 to 6, characterised in that it comprises one or more compounds of the formulae IIa to IIg

   

   

   

   

   

   

   

   in which R⁰ has the meaning indicated in Claim 4.
8. Liquid-crystalline medium according to one of Claims 1 to 7, characterised in that it comprises one or more compounds of the following formulae:

   

   

   

   

   

   

   

   

   

   in which

   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl, alkenyloxy or alkenyl, each having up to 9 C atoms,

   Y¹ denotes H or F,
   alkyl or

   alkyl* in each case, independently of one another, denotes a straight-chain or branched alkyl radical having 1-9 C atoms,
   alkenyl or

   alkenyl* in each case, independently of one another, denotes a straight-chain or branched alkenyl radical having up to 9 C atoms.
9. Liquid-crystalline medium according to at least one of Claims 1 to 8, characterised in that the proportion of compounds of the formula IA in the mixture as a whole is 5 to 40% by weight.
10. Use of the liquid-crystalline medium according to at least one of Claims 1 to 9 for electro-optical purposes.
11. Electro-optical liquid-crystal display containing a liquid-crystalline medium according to at least one of Claims 1 to 9.